Semiconductor device and optical coupling device

ABSTRACT

According to one embodiment, a semiconductor device includes a first semiconductor element having a first surface, a second semiconductor element having a lower surface bonded to the first surface of the first semiconductor element, a gel-like silicone that covers an upper surface of the second semiconductor element, and a resin portion that covers the gel-like silicone and the first surface of the first semiconductor element.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2015-175055, filed Sep. 4, 2015, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor deviceand an optical coupling device.

BACKGROUND

There are optical coupling devices in which a light emitting chip isprovided on a light receiving chip. In such an optical coupling device,the surface of the light emitting chip is typically covered with a firstresin for protection of the light emitting chip. In addition, thesurface of the resin is covered with a second resin.

However, since the first resin and the second resin generally havedifferent thermal expansion coefficients, a strong adhesion between thefirst resin and the second resin leads to a concern that the lightemitting chip will peeled from the light receiving chip due to forceapplied from the second resin portion.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an optical coupling device according toan embodiment.

FIG. 1B is a cross-sectional view taken along line A-A of FIG. 1A.

FIG. 2 is an enlarged cross-sectional view of a main portion with adirection of tension indicated by arrows. The surface of a first resinportion is covered with a second resin portion.

FIG. 3A is a schematic diagram illustrating the arrangement of the firstresin portion when the external shape of a light receiving chip is arectangular shape.

FIG. 3B is a schematic diagram illustrating the arrangement of the firstresin portion when the external shape of a light receiving chip is asquare shape.

FIG. 4 is a schematic cross-sectional view illustrating a vicinity ofthe light emitting chip and the light receiving chip.

FIG. 5 is a schematic enlarged cross-sectional view illustrating aninterface between rubber-like silicone and a resin portion.

DETAILED DESCRIPTION

In general, according to one embodiment, a semiconductor device includesa first semiconductor element having a first surface, a secondsemiconductor element having a lower surface bonded to the first surfaceof the first semiconductor element, a gel-like silicone that covers anupper surface of the second semiconductor element, and a resin portionthat covers the gel-like silicone and the first semiconductor element.

Hereinafter, embodiments will be described with reference to theaccompanying drawings.

(First Embodiment)

FIG. 1A is a perspective view of an optical coupling device 1 accordingto the first embodiment, and FIG. 1B is a cross-sectional view takenalong line A-A of FIG. 1A. Here, the optical coupling device 1 includesa first pad 3, a second pad 4, and a third pad 5 which are arranged on asubstrate 2 so as to be separated from each other, a light receivingchip 6 provided on the first pad 3, a light emitting chip 7 provided onthe light receiving chip 6, a first metal oxide semiconductor fieldeffect transistor (MOSFET) 8 provided on the second pad 4, a secondMOSFET 9 provided on the third pad 5, a gel-like silicone 10 that coversthe surface of the light emitting chip 7, and a resin portion 11 thatcovers the surface of the gel-like silicone 10. The first MOSFET 8 andthe second MOSFET 9 are, for example, power semiconductor elements suchas an IGBT.

In the optical coupling device 1, the light emitting chip 7 converts aninput signal into an optical signal, the light receiving chip receivesthe optical signal in an electrically insulated state (the lightemitting chip and light receiving chip are electrically isolated fromeach other) and converts the received optical signal into an electricalsignal, and the first MOSFET 8 and the second MOSFET 9 drive a load (notspecifically depicted) based on the electrical signal.

In the optical coupling device 1 illustrated in FIGS. 1A and 1B, thefirst MOSFET 8 and the second MOSFET 9 are integrated components, butthe first MOSFET 8 and the second MOSFET 9 may be achieved using asemiconductor element separated from the optical coupling device 1.

The substrate 2 includes a first region 2 b on one end side of a surface2 a in a first direction (depicted as the x direction), and a secondregion 2 c on the other end side. That is, first region 2 b is on oneend of the substrate 2 and the second region 2 c is on another end ofthe substrate 2. FIG. 1A depicts the first region 2 b on the left-pageside of substrate 2 and the second region 2 c on the right-page side ofsubstrate 2. In addition, a pattern 18 is provided on a rear surface 2 dof substrate 2. A first terminal 12 and a second terminal 13 are in thefirst region 2 b, and a third terminal 14 and a fourth terminal 15 arein the second region 2 c. The first terminal 12 is connected to an anodeof the light emitting chip 7 through a bonding wire 16, and the secondterminal 13 is connected to a cathode of the light emitting chip 7through another bonding wire 16. The third terminal 14 is a powerterminal, and the fourth terminal 15 is a ground terminal. The thirdterminal 14 and the fourth terminal 15 are electrically connected to thepattern 18 through separate contacts 17—that is, one contact 17 connectsthird terminal 14 to the pattern 18 and a different contact 17 connectsfourth terminal 15 to the pattern 18. The patterns 18 are alsoelectrically connected to the second pad 4 and the third pad 5 throughseparate contacts 17. In addition, bonding wires 16 for connection thelight receiving chip 6 to each of the first and second MOSFETs 8 and 9and a bonding wire 16 for connecting the first and second MOSFETs 8 and9 are provided.

The light emitting chip 7 may be a semiconductor device with a singlelight-emitting element (such as a light emitting diode (LED)) or may bea single semiconductor element package accommodating a substrate onwhich one or more light-emitting elements is mounted and a substrate onwhich a peripheral circuit for operating the light-emitting element(s)is mounted. The light receiving chip 6 is a semiconductor elementincluding a light-receiving element, such as a photodiode.

A light emitting surface of the light emitting chip 7 is arranged toface a light receiving surface on the upper surface side of the lightreceiving chip 6. The light emitting chip 7 and the light receiving chip6 are bonded to each other using, for example, a transparent adhesivemember 19 obtained by hardening a paste-like, transparent silicone. Theterm “transparent” as used herein refers to being transmissive withrespect to an emission wavelength of light emitted by the light emittingchip 7. The light emitting chip 7 is stacked on the light receiving chip6, and the light emitting surface of the light emitting chip 7 and thelight receiving surface of the light receiving chip 6 are arrangedfacing each other across a short distance. Thereby, light from the lightemitting chip 7 can be received by the light receiving chip 6 withoutsubstantial loss, and thus optical coupling characteristics providinglight receiving efficiency are improved.

As illustrated in FIG. 1B, gel-like silicone 10 covers the surface ofthe light emitting chip 7 and a portion of the bonding wire 16 connectedto the upper surface of the light emitting chip 7. As described later,the gel-like silicone 10 has a property of being lower in hardness thana rubber-like silicone—that is, softer in comparison.

The gel-like silicone 10 is able to be flexibly change shape inaccordance with stresses or strains resulting from variations inenvironmental conditions such as temperature and humidity. Accordingly,the gel-like silicone 10 functions as a tension relaxing member. Thegel-like silicone 10 may be either transparent or opaque to the emissionwavelength.

As illustrated in FIG. 1B, the resin portion 11 covers the surface ofthe gel-like silicone 10 and the surface of the light receiving chip 6,and covers the surfaces of the first MOSFET 8 and the second MOSFET 9.The resin portion 11 serves to encapsulate the light receiving chip 6and the light emitting chip 7 and covers the outer surface of thegel-like silicone 10. The resin portion 11 is formed of an epoxy resinmixed with, for example, particulate carbon or titanium dioxide (TiO₂).The resin portion 11 has a light shielding property such that light fromthe outside of the optical coupling device 1 does not enter the silicone10. That is, the resin portion 11 is formed of a material not beinglight transmissive with respect to light emitted from the light emittingchip 7.

In the related art, the surface of the light emitting chip 7 is coveredwith rubber-like silicone. In order to increase adhesiveness betweenthis rubber-like silicone and resin similar to resin portion 11 (e.g.,an epoxy resin), it is typically preferable that plasma cleaning beperformed on the surface of the rubber-like silicone prior to coveringwith the resin similar to resin portion 11. In the plasma cleaning, thesurface to be cleaned is exposed to electrons and ions having highenergy, and typically a portion of the chemical bonds on the outermostsurface of the object to be cleaned will be broken, thereby allowing theadhesiveness of the surface to be improved.

However, when the resin portion 11 is attached to the surface of therubber-like silicone after plasma cleaning, adhesiveness between thissilicone and the resin portion 11 is greatly increased, and thus thereis a concern that the light emitting chip 7 might, as a result of theexcessive adhesiveness between the rubber-like silicone and the resinportion 11, be peeled (loss of adhesion between light emitting chip 7and the directly contacting rubber-like silicone or adhesion betweenlight emitting chip 7 and transparent resin 19). FIG. 2 is a diagramillustrating a direction of tension which is indicated by arrows y1 andy2 when the light emitting chip 7 is stacked on the light receiving chip6, the surface of the light emitting chip 7 is covered with therubber-like silicone 10, the surface of the silicone 10 is subjected toplasma cleaning, and the surface of the silicone 10 is covered with theresin portion 11.

When the silicone 10 is rubber-like rather than gel-like and is coveredwith the resin portion 11 that is formed of an epoxy resin, the(rubber-like) silicone 10 has a thermal expansion coefficient higherthan that of the epoxy resin, and thus the silicone 10 expands more thanthe resin portion 11 at the time of molding the resin portion 11 atelevated temperatures. As a result, the silicone 10 is pressed againstthe resin portion 11, and thus the silicone 10 and the resin portion 11are firmly bonded to each other, thereby improving adhesiveness.Thereafter, when temperature falls, there is a tendency for the silicone10 to contract in a direction of the arrow y1 of FIG. 2. However, whenadhesiveness between the silicone 10 and the resin portion 11 is high,an interface between the silicone 10 and the resin portion 11 is notmoved, and thus a tension force drawing the light emitting chip 7 in adirection of the arrow y2 is applied. As a result, the transparentadhesive member 19 including the light emitting chip 7 bonded to thelight receiving chip 6 may be peeled. When the light emitting chip 7 ispeeled, a positional relationship between the light emitting surface andthe light receiving surface is deviated, and thus a greater portion ofemitted light is not successfully received by the light receiving chip6, which results in a deterioration in optical coupling characteristics.

In this manner, when plasma cleaning is performed in order to improveadhesiveness between the silicone 10 and the resin portion 11 when usinga rubber-like silicone, the light emitting chip 7 is more easily peeled.

On the other hand, when the resin portion 11 is attached onto thesurface of the rubber-like silicone 10 without first performing plasmacleaning, the rubber-like silicone 10 has a contraction rate higher thanthat of the resin portion 11 formed of an epoxy resin, and thus peelingtends to occur at the interface between the rubber-like silicone 10 andthe resin portion 11. When the silicone 10 is peeled off from the resinportion 11, the bonding wire 16 on the upper surface of the lightemitting chip 7 may more easily be disconnected or damaged.

In the present embodiment, a gel-like silicone is adopted rather thanadopting a rubber-like silicone for the silicone 10 element. Thegel-like silicone is a material which is more easily plasticallydeformed as it has a lower hardness value than an epoxy resin or arubber-like silicone. The value of hardness of the gel-like silicone canbe measured by, for example, a durometer. Regarding the gel-likesilicone used in the present embodiment, the value of hardness (hardnessvalue) measured by a durometer according to JIS K 6253 or JIS K 7215(type A) (Japanese Industrial Standards) is within a range of from 10 to24. An experiment was conducted in which the hardness value of thesilicone 10 element was varied. The experiment indicates there is atendency for a gel-like silicone to be deformed when the hardness valueis less than 10, and thus it can be understood that there is a concernthat the external shape of such a soft silicone material may be unableto be stably maintained once the material is applied. A silicone havinga more stable shape can be provided when the hardness value is equal toor greater than 16. In addition, when the hardness value is greater than24, the silicone may be considered to be excessively hardened, whichresults in a degradation of the adhesiveness of the silicone withrespect to the resin portion 11, and thus there is a concern of aninterfacial gap being generated.

For reference, resin portion 11 formed of an epoxy resin has a hardnessvalue of 75 as measured by a durometer. When the hardness value of thegel-like silicone material is within a range of from 10 to 24,adhesiveness between the silicone 10 and the resin portion 11 isacceptable. Thus, peeling or the like at the surface of the silicone 10did not occur before and after an accelerated life test such as apressure cooker test (PCT). It is preferable that the hardness value ofthe resin portion 11 is three or more times the hardness value of thesilicone 10, that is, the hardness value of the resin portion 11 ispreferably equal to or greater than at least 30.

According to the experiments, when the light emitting chip 7 is coveredwith a gel-like silicone having a hardness value of 10 to 24, peeling ofthe light emitting chip 7 does not significantly occur even when anaccelerated life test such as a pressure cooker test (PCT) is performedin a high-temperature, high-humidity atmosphere. In some embodiments,the hardness value of the gel-like silicone is preferably in the rangeof 16 to 24.

In the gel-like silicone 10, there is a tendency for a contact interfacebetween the silicone 10 and the resin portion 11 to be flexibly moveddepending on tension. Accordingly, even when tension is applied to aportion of the silicone 10, the silicone 10 functions as a tensionrelaxing member by releasing tension in the vicinity thereof by flexing.In addition, when the gel-like silicone 10 is used, adhesiveness withrespect to the resin portion 11 is increased compared to a case wherethe rubber-like silicone 10 is used, and thus it is not necessary toperform plasma cleaning on the surface of the gel-like silicone 10.Thereby, it is possible to simplify a manufacturing process by omissionof the plasma cleaning processing.

However, plasma cleaning may still be performed on the gel-like silicone10 is desired. The flexibility of the interface between the silicone 10and the resin portion 11 is not significantly damaged by the plasmacleaning, and the gel-like silicone 10 can continue to function as atension relaxing member.

In addition, plasma cleaning may be performed before the gel-likesilicone 10 is formed. That is, plasma cleaning is performed on thesurfaces of the light emitting chip 7 and the light receiving chip 6before forming the gel-like silicone 10, and thus the wettability ofthese surfaces can be improved, and the gel-like silicone 10 more easilyattached to these surfaces.

As the thickness of the gel-like silicone 10 becomes larger, it becomes,in general, easier to relax tension, and thus, all other things beingequal, it is preferable that the silicone 10 be as thick as possible. Asillustrated in FIG. 1, for example, when the external shape of the lightreceiving chip 6 is a rectangular shape and the external shape of thelight emitting chip 7 stacked thereon is a square shape, it ispreferable to arrange the light emitting chip 7 at the substantiallycenter portion of the upper surface of the light receiving chip 6 and toarrange the silicone 10 on substantially entire upper surface of thelight receiving chip 6, as illustrated in a schematic diagram of FIG.3A. In this case, the silicone 10 is formed to be thicker in the seconddirection y on the side of a long side of the light receiving chip 6,and thus it is possible to further prevent the light emitting chip 7from being peeled along this direction.

Meanwhile, the external shape of the light receiving chip 6 is notnecessarily limited to being a rectangular shape, and may be, forexample, a square shape. In this case, as illustrated in a schematicdiagram of FIG. 3B, it is preferable to arrange the light emitting chip7 at the substantially center portion of the upper surface of the lightreceiving chip 6 and to equally arrange the silicone 10 in fourdirections.

In this manner, in the first embodiment, the light emitting chip 7 isstacked on the light receiving chip 6, the surface of the light emittingchip 7 is covered with the gel-like silicone 10, and the surface of thegel-like silicone 10 is covered with resin portion 11 formed of an epoxyresin. For this reason, a contact interface between the gel-likesilicone 10 and the resin portion 11 is flexible, and the gel-likesilicone 10 functions as a tension relaxing member. It is thus possibleto prevent the light emitting chip 7 from being peeled even whenenvironmental conditions such as temperature and humidity vary duringoperation of the light emitting device.

(Second Embodiment)

According to a second embodiment a light emitting chip 7 is preventedfrom being peeled while using a rubber-like silicone 10. Rubber-likesilicone material has a hardness value greater than gel-like siliconematerial, for example, rubber-like silicone material has a hardnessvalue greater than or equal to 25 as measured by a durometer inaccordance with at least one of JIS K 6253 and JIS K 7215 (type A).

An optical coupling device 1 according to the second embodiment isconfigured in a similar manner as that of FIG. 1. FIG. 4 is a schematiccross-sectional view illustrating the vicinity of a light emitting chip7 and a light receiving chip 6. As illustrated in FIG. 4, the surface ofthe light emitting chip 7 stacked on the light receiving chip 6 andportions of bonding wires 16 connected to the light emitting chip 7 andthe light receiving chip 6 are covered with the rubber-like silicone 10.The rubber-like silicone 10 is covered with a resin portion 11 that isformed of an epoxy resin or the like. FIG. 5 is a schematic enlargedcross-sectional view illustrating the vicinity of an interface betweenthe rubber-like silicone 10 and the resin portion 11.

The rubber-like silicone 10 according to the second embodiment hasdifferent thicknesses on the upper surface side and the side surfaceside of the light emitting chip 7. More specifically, the thickness ofthe rubber-like silicone 10 on the upper surface side of the lightemitting chip 7 is smaller than the thickness on the side surface side.The rubber-like silicone 10 can be attached onto the surface of thelight emitting chip 7 in a high temperature state, which increasesflexibility of the rubber-like silicone 10, and thus it is possible toattach a larger amount of silicone material to the side surface side ofthe light emitting chip 7 than to the upper surface side of the lightemitting chip 7.

In the second embodiment, after the surface of the light emitting chip 7has been covered with the rubber-like silicone 10, the resin portion 11is formed thereon without performing plasma cleaning on the surface ofthe rubber-like silicone 10. The resin portion 11 is formed of, forexample, an epoxy resin. When the resin portion 11 is formed withoutperforming plasma cleaning on the surface of the rubber-like silicone10, the rubber-like silicone 10 will expand more than the resin portion11 due to the high temperatures during molding. For this reason,adhesiveness between the rubber-like silicone 10 and the resin portion11 is somewhat improved. When the temperature is lowered upon thetermination of the molding process used in forming the resin portion 11,the rubber-like silicone 10 contracts by a greater amount than the resinportion 11. Since the rubber-like silicone 10 is formed to be thicker onthe upper surface side of the light emitting chip 7 than that on theside surface side of the light emitting chip 7, the degree ofcontraction is asymmetrical in that the total amount of contraction ofthe silicone material on the side surface side will be greater than thetotal amount of contraction on the silicone material on the uppersurface side. The overall amount of contraction is increased because thethickness of the silicone 10 on the side surface side is larger thanthat on the upper surface side.

Accordingly, on the side surface side of the light emitting chip 7, alarger first gap portion 21 is formed between the rubber-like silicone10 and the resin portion 11, as illustrated in FIG. 5. The first gapportion 21 is larger than a second gap portion 22 between therubber-like silicone 10 and the resin portion 11 on the upper surfaceside of the light emitting chip 7. The second gap portion 22 is formedbetween the rubber-like silicone 10 and the resin portion 11, and thusthe tension of the rubber-like silicone 10 pulling the light emittingchip 7 is relaxed, thereby preventing the light emitting chip 7 frombeing peeled.

Since the thickness of the rubber-like silicone 10 is small on the uppersurface side of the light emitting chip 7, the amount of contraction ofthe silicone 10 is small, and a large gap is not formed between thesilicone 10 and the resin portion 11. Accordingly, it is possible toprevent the bonding wire 16 which is arranged to contact the uppersurface side of the light emitting chip 7 from being disconnected.

Additionally, plasma cleaning may be performed on a portion of therubber-like silicone 10, specifically, only on the upper surface side ofthe light emitting chip 7 might be plasma cleaned before the surface ofthe rubber-like silicone 10 is covered with the resin portion 11, andadhesiveness between the silicone 10 and the resin portion 11 on theupper surface side of the light emitting chip 7 may be thereby improved.Thus, even when the rubber-like silicone 10 contracts, the second gapportion 22 is less likely to be generated between the rubber-likesilicone 10 and the resin portion 11. When the rubber-like silicone 10and the resin portion 11 are provided in contact with each other,tension of the contracting rubber-like silicone 10 acts in a directionin which the light emitting chip 7 is pulled from the light receivingchip 6. However, the thickness of the rubber-like silicone 10 is smallon the upper surface side of the light emitting chip 7, and thus theresulting peeling force (tension) produced by the rubber-like silicone10 is small. Accordingly, there is an insignificant tendency for thelight emitting chip 7 to be peeled. In addition, when the rubber-likesilicone 10 and the resin portion 11 are provided in contact with eachother on the upper surface side of the rubber-like silicone 10, it iseasier to prevent the bonding wire 16 from being disconnected.

In this manner, in the second embodiment, the thickness of therubber-like silicone 10 on the side surface side of the light emittingchip 7 is larger than that on the upper surface side of the lightemitting chip 7, and thus a gap between the rubber-like silicone 10 andthe resin portion 11 on the side surface side is larger than that on theupper surface side. Accordingly, it is possible to reduce peeling forceon the light emitting chip 7 and to prevent the light emitting chip 7from being peeled. In the second embodiment, the light emitting chip 7can be prevented from being peeled while using the rubber-like silicone10, and thus it is possible to prevent the light emitting chip 7 frombeing peeled without changing the material of the silicone.

In the first and second embodiments described above, a description hasbeen given of a structure for preventing peeling from occurring when thelight-emitting element 7 is bonded onto the light receiving chip 6, butthe light receiving chip 6 and the light-emitting element 7 are notessential components. The exemplary embodiments can be applied tovarious semiconductor devices in which a second semiconductor element isbonded onto a first semiconductor element, and the specific of the firstsemiconductor element and the second semiconductor element do notparticularly matter. That is, any two elements which are bonded togetherfor packaging within resin materials may incorporate the disclosedembodiments so as to prevent or reduce peeling, delamination, de-bondingor the like of the two bonded elements. As used herein, “value ofhardness” or “hardness value” of a material is the value measured inaccordance with at least one of JIS K 6253 and JIS K 7215 (type A)(Japanese Industrial Standards) as applicable.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein maybe made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A semiconductor device, comprising: a substratehaving a first surface side and a second surface side opposite the firstsurface side, the first surface side including a first surface region ata first end of the substrate in a first direction and a second surfaceregion on a second end of the substrate in the first direction oppositethe first end; a wiring pattern on the second surface side of thesubstrate; a first terminal and a second terminal on the substrate inthe first surface region; a third terminal and a fourth terminal on thesubstrate in the second surface region; a first semiconductor elementhaving a first surface, the first semiconductor element being bonded tothe substrate on the first surface side between the first and secondsurface regions; a second semiconductor element having a lower surfacebonded to the first surface of the first semiconductor element; a firstbonding wire connecting the first terminal and anode terminal of thesecond semiconductor element; a second bonding wire connecting thesecond terminal and a cathode terminal of the second semiconductorelement; a third semiconductor element bonded to the substrate on thefirst surface side between the first semiconductor element and thesecond surface region; a third bonding wire connecting the firstsemiconductor element and the third semiconductor element, the thirdbonding wire being connected to a pad on the first surface of the firstsemiconductor element; a silicone gel covering an upper surface of thesecond semiconductor element and contacting a portion of the firstsurface of the first semiconductor device; and a resin portion coveringthe silicone gel, the first semiconductor element, the thirdsemiconductor element, the first bonding wire, the second bonding wire,the third bonding wire, the first surface region, and the second surfaceregion, wherein the resin portion has a durometer-measured hardnessgreater than a durometer-measured hardness of the silicone gel, thefirst semiconductor element includes a light receiving element facingthe first surface of the first semiconductor element, the secondsemiconductor element includes a light emitting element that emits lightat the lower surface of the second semiconductor element, and thesilicone gel is opaque at a wavelength of light emitted by the lightemitting element.
 2. The semiconductor device according to claim 1,wherein the resin portion is an epoxy resin.
 3. The semiconductor deviceaccording to claim 1, wherein the first semiconductor element is bondedto the second semiconductor with a transparent silicone material havinga distinct composition from the silicone gel.
 4. The semiconductordevice according to claim 1, wherein the resin portion is opaque at awavelength of light emitted by the light emitting element.
 5. Thesemiconductor device according to claim 1, wherein a thickness of thesilicone gel on the upper surface of the second semiconductor element isgreater than a thickness of the silicone gel on a side surface of thesecond semiconductor element, the thicknesses being respectivelymeasured along a direction normal to the upper surface and the sidesurface.
 6. The semiconductor device according to claim 1, wherein aportion of the first and second bonding wires pass through the siliconegel.
 7. An optical coupling device, comprising: a substrate having afirst surface side and a second surface side opposite the first surfaceside, the first surface side including a first surface region at a firstend of the substrate in a first direction and a second surface region ona second end of the substrate in the first direction opposite the firstend; a wiring pattern on the second surface side of the substrate; afirst terminal and a second terminal on the substrate in the firstsurface region; a third terminal and a fourth terminal on the substratein the second surface region; a light receiving chip and a lightemitting chip on the first surface side of the substrate between thefirst and second surface regions and bonded to each other in a facingarrangement such that light from the light emitting chip is emitted fromthe light emitting chip towards the light receiving chip; a firstbonding wire connecting the first terminal and anode terminal of thelight emitting chip; a second bonding wire connecting the secondterminal and a cathode terminal of the light emitting chip; a MOSFETchip bonded to the substrate on the first surface side between the lightreceiving chip and the second surface region; a third bonding wireconnecting the light receiving chip and the MOSFET chip, the thirdbonding wire being connected to a pad on an upper surface of thelight-receiving chip facing the light emitting chip; a silicone gelcovering an upper surface and a side surface of the light emitting chipand directly contacting the upper surface of the light receiving chip;and an epoxy resin portion covering an outer surface of the silicone geland encapsulating the light receiving chip, the light emitting chip, theMOSFET chip, the first bonding wire, the second bonding wire, the thirdbonding wire, the first surface region, and the second surface region,wherein the epoxy resin portion has a durometer-measured hardnessgreater than a durometer-measured hardness of the silicone gel, thedurometer-measured hardness of the silicone gel is one-third or less ofthe durometer-measured hardness of the epoxy resin portion, and thesilicone gel is substantially opaque to the light emitted by the lightemitting chip.
 8. The optical coupling device according to claim 7,wherein a thickness of the silicone gel on the upper surface of thelight emitting chip is greater than a thickness of the silicone gel onthe side surface of the light emitting chip, the thicknesses beingrespectively measured along a direction normal to the upper surface andthe side surface.
 9. The optical coupling device according to claim 7,wherein a portion of the first and second bonding wires pass through thesilicone gel.